1. Field of the Invention
The invention relates generally to materials for making dental prostheses and restorations such as inlays, onlays, veneers, crowns, and bridges. Particularly, the materials include one universal opaque, one universal pressable ingot, and one universal veneering porcelain that can be used interchangeably to manufacture a prosthesis or restoration using different techniques. This includes porcelain-fused-to-metal (PFM), press-to-metal (PTM), and pressed or computer-aided-manufacturing (CAM) machined all-ceramic techniques.
2. Brief Description of the Related Art
There are various methods known in the dental arts for making dental prostheses and restorations. By the term, “prosthesis” or “restoration” as used herein, it is meant any product that replaces or restores lost tooth structure, teeth, or oral tissue including, but not limited to, implant stents, bite registrations, crown and bridges, fillings, baseplates, splints, denture liners, custom trays, artificial teeth, repairs for natural teeth, veneers, denture repairs, denture relines, retainers, orthodontic components, provisional dental devices, inlays, onlays, orthodontic appliances, temporary dentures, temporary partial dentures, maxillofacial prostheses, obturators, and occular prostheses, and the like.
Conventional dental prostheses may include a metal coping or substructure to provide additional mechanical strength and durability to the prosthesis. In practice, the metal copings are covered with glass or ceramic-based materials that mimic the color and form of natural teeth. The metal copings support the glass or ceramic-based veneering layer and provide enhanced structural strength and toughness to the restoration.
A traditional method for making a dental prosthesis is known as “porcelain-fused-to-metal” (PFM). Typically, the process of making a PFM restoration involves applying three layers of porcelain onto a metal framework. Initially, an opaque porcelain composition, in either powder or paste form, is applied over a metal framework to form an opaque layer that masks the metal. Subsequently, a dentin body layer is built up using dentin porcelain powder and then a third layer simulating the incisal portion of a natural tooth is built up using enamel porcelain powder. In PFM restorations, the layering of the wet porcelain compositions is traditionally done by hand. The porcelain compositions are fired at high temperatures to form hard and durable dentin and incisal layers having the appearance of natural teeth. Other porcelain materials, such as opaceous dentin, dentin modifier, and stain porcelain, margin, and final margin porcelains can be added to enhance the esthetics of the final dental restoration. The PFM restorations can be finished by applying a thin layer of glaze porcelain to provide a glossy surface finish.
One drawback with PFM restorations is that the dark-colored margin may be exposed at the gum line and the restoration may not have the most pleasing esthetics. To improve esthetics, “all-ceramic” systems have been developed. These all-ceramic systems use a ceramic core in place of the metal framework. The ceramic core is coated with at least one porcelain layer. In one technique, an all-ceramic prosthesis having a core is fabricated using a hot-pressing technique. (For example, the Empress™ prosthetic system (Ivoclar Vivadent AG, Liechtenstein) was developed.) An alternative way of fabricating all-ceramic cores is to use a computer-aided-manufacturing (CAM) method and machine directly on a ceramic block as described in the Cerec™ system (Sirona Dental Systems GmbH, Germany). While all-ceramic prostheses may offer improved esthetics over PFM restorations, the all-ceramic prostheses tend to be more brittle. Traditionally, all-ceramic prostheses have been limited generally to anterior up to pre-molar applications. Although in recent years, using high strength alumina and zirconia as the core has allowed all-ceramic restorations to be used in posterior and bridge applications.
Another method that has grown in popularity over the last several years is known as the “press-to-metal” (PTM) process. The PTM process involves placing a metal coping or substructure in a mold. The coping is then coated with an opaque porcelain composition which may be in powder or paste form. The opaque coating is followed by wax-up and spruing to form the prosthesis form. The form is then invested in a ceramic investment material, and the wax is burned out. This forms the prosthesis mold. A porcelain layer is fused to the opaque surface by hot-pressing an ingot porcelain material onto the coping contained in the mold at fusing temperatures. The hot-pressed porcelain flows into the burn-out cavity to form the dentin layer. The prosthesis is then divested of the molding material and finished. The result is a strong and tough dental prosthesis having a metal substructure that is veneered with porcelain. The prosthesis has generally good esthetics with integrated transparency that matches the appearance of natural dentition.
Conventional methods for making PFM, PTM, and all-ceramic restorations are described in the patent literature. For example, Kosmos, U.S. Pat. No. 4,741,699 discloses making a porcelain dental restoration having fluorescence that matches the fluorescence of natural teeth. The restoration includes a metal supporting substrate, a body layer, and incisal layer. An aqueous slurry of an opaque porcelain is applied and fired to the metal substrate. A body layer and incisal layer are formed from porcelain powder mixtures containing fluorescent pigment. The powder mixtures comprise a base porcelain, stained porcelain, and fluorescing agent and are applied by hand to build-up the restoration.
Komma et al., U.S. Pat. No. 5,281,563 describes methods for making metal and ceramic dentures. The ceramic powder is applied to the metallic framework as an aqueous slurry and fired at elevated temperatures to produce the prosthesis. Komma notes that it is important that the firing temperature (processing temperature) of the ceramic body be at least 100° C. below the solidus temperature of the material in the metallic framework and the coefficient of thermal expansion of the ceramic body be only very slightly less than that of the metallic material, so that no cracks are produced in the lining layer during firing and cooling down.
Brodkin et al., U.S. Pat. No. 6,428,614 is directed to an opaque porcelain material for making both all-ceramic and porcelain-fused-to-metal (PFM) restorations. The opaque porcelain exhibits a coefficient of thermal expansion (CTE) substantially equal to or slightly above the CTE of the metal to which the porcelain is being applied. The porcelain material is fabricated from a mixture of two frit compositions. The porcelain material has a composition of 48 to 65% SiO2; 10 to 15% Al2O3; 0.5 to 2% CaO; 1.5 to 3% Li2O; 15 to 17% K2O; 4 to about 6% Na2O; and 0.4 to 1% F.
Chu and Banasiak, US Patent Application Publication No. US 2007/0196788 discloses a dental prosthesis having a metal coping that is coated with an opaque coating. A single porcelain layer having an integrated tooth-like translucency is coated over the opaque coating. The porcelain layer is formed of a dentin frit and enamel frit that is sintered into an ingot shape. The weight percent of dentin frit is in the range of 70 to 85% and the weight percent of enamel frit is in the range of 15 to 30%. The resulting restoration has strong substructure that is veneered with porcelain having an integrated transparency.
One major problem with conventional PFM, PTM, and all-ceramic systems available in the marketplace today is that the components of each system are tailored to their own applications. The materials cannot be used interchangeably across the systems due to the thermal incompatibility among the components and/or metal substructure. Hence, systems with various components need to be purchased separately for making different types of restorations. This may cause over-inventory problems and confusion over mixing use of the components in dental laboratories.
It is an object of the present invention to provide an integrated porcelain system having components that can be used interchangeably among porcelain-fused-to metal (PFM), press-to-metal (PTM), and pressed or computer-aided-manufacturing (CAM) machined all-ceramic restorations It is another object of the invention to provide a universal opaque porcelain composition that can be used for making PFM and PTM prostheses. Yet another object of the invention is to provide universal pressable ingots that can be used for making dentin body layers over opaqued metal framework in PTM prostheses and all-ceramic cores. It is still another object of the invention to provide a universal veneering porcelain composition that can be used for making dentin-enamel layers and enamel layers. These and other objects, features, and advantages of the present invention are evident from the following description and illustrated embodiments.